The present invention concerns improved Hall effect devices generally and more particularly relates to improved linearity of interfaces for Hall effect devices. Such Hall effect devices are particularly useful for incorporation into power meters, for placement in ferromagnetic core gaps for metering electrical power being drawn from a power grid.
One use of Hall effect sensors is in power meters designed to measure electrical power consumption. One example of such a power meter arrangement with inclusion and use of a Hall effect sensor is disclosed in commonly owned U.S. Pat. No. 5,694,103, issued to Goodwin, et al.
Goodwin, et al. discloses a ferromagnetic core arrangement having a central core leg defining a core gap in which a Hall effect sensor is located. The sensor produces a measurable Hall voltage that is proportional to the magnetic flux density within the gap and to the bias current supplied to the sensor. If the bias current is made proportional to the instantaneous line voltage, the Hall output becomes a measure of power. Hence, the power meter may be used for measuring power consumption from an associated power grid.
In general, additional or complicated stages in any sensing or metering system can create the possibility of reduced signal quality and/or higher costs. Also, certain components inherently have the potential to interject certain noise signals into an overall system. For example, operational amplifiers may have input offset voltages and Hall effect devices may have output offset voltages which could otherwise affect the linearity of any system in which they are used.
One particular potential problem can occur at relatively low magnetic flux levels. In such instances, the output voltage of the Hall device would ordinarily be relatively small as compared to potential offset voltage levels. Hence, under such conditions, particular problems may exist with obtaining quality metering, especially concerning the linearity of the collective system
Still another potential source of noise signals is the occurrence of common mode voltages. These typically must otherwise be rejected by following system electronics, or otherwise they will appear at the system level as noise.
Yet another potential difficulty causing system degradation arises from temperature effects and component values. It is especially difficult to address certain such problems in the context of reducing costs, since relatively lower cost components may sometimes have wider specification tolerances and lesser desired responses to temperature effects. In other words, attempts to use lower cost components may in some instances exacerbate existing system problems.
The entire disclosure of the above-referenced issued U.S. Pat. No. 5,694,103 is fully incorporated herein by reference.
The present invention recognizes and addresses various of the foregoing problems, and others, concerning Hall effect devices. Thus, broadly speaking, a principal object of this invention is improved Hall effect device operations. More particularly, a main concern is improved interfaces with Hall effect devices.
It is therefore another particular object of the present invention to provide interfaces having improved, high linearity for Hall effect devices. In such context, it is an overall objective to reduce and minimize offset effects without the use of complicated electronic circuits.
Similarly, another present object is to virtually eliminate common mode voltages that must otherwise be rejected by more expensive system electronics, or otherwise appear at a system level as noise.
Still a further more particular object of the present invention is to provide an improved interface system which provides exceptional performance at very low cost. At the same time, it is an object to provide such an improved system which is very robust to temperature effects and component values.
Additional objects and advantages of the invention are set forth in, or will be apparent to those of ordinary skill in the art from, the detailed description herein. Also, it should be further appreciated that modifications and variations to the specifically illustrated and discussed features hereof may be practiced in various embodiments and uses of this invention without departing from the spirit and scope thereof, by virtue of present reference thereto. Such variations may include, but are not limited to, substitution of equivalent means and features for those shown or discussed, and the functional or positional reversal of various parts, features, or the like.
Still further, it is to be understood that different embodiments, as well as different presently preferred embodiments, of this invention may include various combinations or configurations of presently disclosed features or their equivalents (including combinations of features or configurations thereof not expressly shown in the figures or stated in the detailed description).
One exemplary embodiment of the present invention relates to an improved Hall effect device interface using a biasing technique for such Hall effect device in conjunction with the connection of the substrate of the Hall effect device, which technique almost totally eliminates any undesirable offset effects which are due to non-symmetries in the device. Such non-symmetries can be anything that causes the current density to be non-uniform throughout the Hall device channel, such as mis-alignment of the layout, imperfections, or parasitic components of the device. Such non-symmetries may become particularly significant at relatively low magnetic flux levels, as referenced above.
Still additional exemplary embodiments of the present invention may make use of first and second levels of modulation with reference to the line frequency, for further enhancing offset rejection of the overall system. For example, a first level of modulation may be used to synchronize input control switches of the Hall effect device to the line frequency. Such modulation has the desired benefit of cancelling a large portion of the offsets from the Hall effect device itself and from the subsequent electronics. Such is particularly true when utilized with a second level of modulation generated from and synchronized with a calibrated output of the system.
Yet another construction comprising an exemplary embodiment of the present invention makes use of a differential drive circuit to invert a voltage present at one input of a Hall effect sensor so as to apply the inverted voltage to the other input of the sensor. Such arrangement desirably generates a fully symmetrical electrical gradient in the Hall effect channel with a virtual ground at the midpoint.
Additional embodiments may comprise various combinations of the above referenced exemplary features (or their equivalents), and/or other features.
It is to be understood that the subject invention likewise encompasses the use of methodologies and techniques which correspond with practice of the physical apparatuses and devices otherwise disclosed herein.
Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, methods, techniques, and others, upon review of the remainder of the specification.